It is known to apply plasma excitation fields at two different frequencies to a region of a vacuum chamber for plasma processing a workpiece, wherein the region is coupled to a gas that the fields convert into the processing plasma. The workpiece is usually a semiconductor wafer, or dielectric plate and the plasma is involved in forming integrated circuit features on the workpiece. High frequency RF power (having a frequency in excess of approximately 10 MHz) typically controls the density of the plasma, i.e., the plasma flux, while RF power having a low to medium frequency (in the range of 100 kHz to approximately 10 MHz) typically controls the energy of ions in the plasma and incident on the workpiece. The excited plasma in these processors typically dry etches the workpiece, but in some instances results in materials being deposited on the workpiece. Typically, the AC plasma excitation fields are supplied to the region by a pair of spaced electrodes in the chamber or one electrode in the chamber and a coil, located outside the chamber. (It is to be understood that the term “reactance”, when used in the present document in connection with a vacuum plasma processing chamber, refers to an electrode or a coil for supplying AC plasma excitation fields to a plasma in the chamber.)
The commonly assigned, copending application of Vahedi et al., Ser. No. 10/180,978, filed Jun. 27, 2002 discloses a processor wherein two different frequencies are simultaneously applied to a vacuum plasma processing chamber bottom electrode (i.e., the electrode on which a workpiece being processed is disclosed), while a top electrode of the chamber is grounded.
As the size of the features continues to decrease, there are increased requirements for precise control of various parameters of the plasma processing a workpiece. Amongst the plasma parameters requiring precise control are the plasma chemistry (i.e., types of ionic and radical species), the plasma flux and the ion energy of the plasma incident on the substrate. With the shrinking feature sizes and use of new materials in fabrication of integrated circuits, windows involved in processing the workpiece are decreasing in size, while pushing the limits on presently available plasma processors, particularly processors for etching. The shrinking feature sizes and requirements for new materials limit the use of the same reactor, i.e., vacuum processing chamber, for different etch applications.
The copending Dhindsa et al. application provides these results by exciting the plasma with electric energy at several frequencies, such that excitation of the plasma by the several frequencies simultaneously causes several different phenomena to occur in the plasma. By exciting the plasma with electric energy at three different frequencies, such as approximately 2 MHz, 27 MHz and 60 MHz, precise control of the chemistry, density and ion energy of the plasma for processing a workpiece is provided. In one embodiment of the co-pending Dhindsa et al. application, a plasma excitation source arrangement applies several frequencies to the bottom electrode, while a top electrode, opposite from the bottom electrode, is grounded. The plasma excitation source arrangement of the co-pending Dhindsa et al. application includes a broad disclosure of circuitry for (1) providing an impedance match between sources of the frequency and the plasma, and (2) decoupling the frequencies associated with the different sources from each other. The plasma resulting from the source arrangement of the co-pending Dhindsa et al. application can include at least one variable frequency RF source, at least one fixed frequency RF source, and at least one variable power RF source.